Strings of individually pocketed springs are known. Multiple such strings of springs have been combined in a parallel fashion to create a spring assembly. Each of the coil springs of the string is contained within an individual pocket of fabric which extends from the top to the bottom of the spring. Typically, each of the springs within the string has identical features or characteristics. Consequently, bedding or seating products made from identical strings of pocketed springs have uniform characteristics throughout the bedding or seating product.
Published PCT patent application No. WO 99/35081 discloses a mattress having two layers of pocketed springs. Each of the springs in each layer is individually pocketed, and the springs of the upper layer are directly above the corresponding springs of the lower layer. A pair of such corresponding springs, one above the other, are enclosed in an external cover and separated from one another by a generally horizontal partition wall of fabric. The springs of the upper layer are "softer" than the springs of the lower layer. Thus, this mattress is able to provide a soft upper layer and a harder lower supporting layer. By using springs having different characteristics in the different layers of the mattress, differing degrees of firmness may be imparted to the mattress.
In order to make such a mattress, a large number of coil springs must be used. For every lower spring, there must be a corresponding upper spring directly above it. Additionally, each of these springs must be individually pocketed. This large number of coil springs and the effort required to individually pocket each spring increases the cost of manufacturing the mattress, and also the time required to manufacture it. Additionally, the upper spring may move sideways relative to the lower spring, causing the springs to move out of alignment with one another and create a bump, indentation or uneven spot in the mattress. Another possibility with such a mattress is that the spring of the upper layer may rotate relative to the spring of the lower layer, reducing the ability of the mattress to function as desired.
Therefore, it has been one objective of the present invention to provide a multilayered bedding or seating product made of individually pocketed springs without using different springs for the upper and lower layers.
Another objective of the present invention has been to provide a pocketed bedding or seating product made of a plurality of similarly constructed strings of pocketed springs joined together.
Still another objective of the present invention has been to provide a pocketed bedding or seating product which may be custom manufactured for a particular application.